Research in the Psychoacoustics Laboratory is concerned with the relation between intensity resolution, masking and loudness. These topics can be loosely organized as a triangle. Until recently, our work focused on intensity resolution and masking, but we have now shifted to the loudness corner of the triangle. There is a remarkable lack of consensus in the loudness research community regarding some of the techniques for measurement of loudness in clinical research, while many of those in the masking research community who would reject all of the techniques because they are subjective. On the other hand, the obvious relevance of loudness in our everyday lives has led to the development of ANSI and ISO standards supported by computational models that make precise predictions. There is no comparable consensus regarding prediction of masked thresholds or intensity difference limens. We are currently focusing on issues directly related to the measurement of the loudness of broadband sounds in listeners with sensorineural hearing loss. These measurements are important for hearing aid research, but may be among the most difficult loudness measurements to make. We are attacking the problem using techniques borrowed from the masking literature.
The laboratory is equipped with two double-walled, sound-treated booths. The main booth is subdivided into four cubicles for simultaneous testing of four subjects. Each cubicle is controlled by a separate PC equipped with a 24-bit Card Delux sound card. Stimuli are presented through Sennheiser 250 headphones and responses are obtained using keypads controlled through a serial interface or through a keyboard and mouse. The second booth has a PC with a 24-bit soundcard and an Etymotic ER-10C low-noise microphone system that is used for the measurement of otoacoustic emissions.
The laboratory is directed by
Walt Jesteadt, Ph.D. Stephen T. Neely, D.Sc. works closely with Dr. Jesteadt and other members of the laboratory staff on models of auditory perception. Donna L. Neff, Ph.D. is a frequent collaborator on studies involving stimulus uncertainty and informational masking. Other staff members include Daniel Valente, Ph.D. and Marc Brennan, Ph.D., postdoctoral fellows who split their time between Psychoacoustics and other laboratories. Hongyang Tan, M.S. is a programmer who implements computer models of detection and discrimination, develops special-purpose data analysis software, and aids other members of the laboratory staff with data analysis. Thomas Creutz, B.S., creates and maintains the data-collection software. Both programmers also support several other labs. Suyash Joshi works in the laboratory as a research assistant.
The current focus of this research program is to develop better methodology for the measurement of loudness and to apply the methodology to measurement of the loudness of broadband sounds. Abnormal and uncomfortable loudness is a major cause of rejection of hearing aids, despite the fact that many hearing-aid fitting algorithms are specifically designed to restore normal loudness. Much of our understanding of loudness was gained in basic research using narrowband sounds. To study the loudness of broadband sounds, we need tools that will provide information on the contributions of specific frequency regions to the overall loudness of the sound. We are developing those tools using methods widely used in studies of masking, where the impact of specific stimulus properties on perception is determined by computing the correlation between those stimulus properties and subjects’ responses across many stimulus presentations. By varying the level of noise in specific frequency bands from presentation to presentation and having subjects make loudness judgments, it is possible to determine the relative contributions of the stimulus bands to the total loudness of broadband sounds. We are comparing these measures of perceptual weight to data obtained in loudness matching experiments and to perceptual weights predicted by the Moore and Glasberg (2004) loudness model. Preliminary work with the model suggests that the perceptual-weights measure is highly correlated with specific loudness, the contribution of each frequency to total loudness as predicted by the model. Observed perceptual weights data, however, are not highly correlated with the perceptual weights predicted by the model.
Research in psychoacoustics is concerned with the relation between the physical properties of sound, such as frequency and intensity, and the psychological or perceptual properties, such as pitch and loudness. Physical properties of sound can be readily assessed, but measuring the sensory or perceptual experience evoked by a sound is more difficult. Audiologists are required to make such measurements every day, establishing when sounds can be heard, for example, or how loud they are. Our research program is focused on the problem of using the physical properties of sounds to predict the loudness of sounds in listeners with normal hearing and sensorineural hearing loss. We know a lot about loudness, but most of the work has been done with pure tones rather than broadband sounds like speech. When broadband sounds are too loud, one solution is to reduce the level of the entire sound. For listeners with hearing loss, this may make some parts of the sound inaudible. It would be better to know which frequency regions are making the biggest contribution to loudness and to reduce the levels of those specific frequency regions. We are developing the necessary measurement techniques. They may require more test time than is typically available when adjusting hearing aids, but could be quite useful in hearing aid research. We are particularly interested in identifying young adults with mild and moderate hearing loss in the Omaha area who would be willing to serve as paid subjects in these studies. If you are interested, please call 402 498-6705.
Copies of our waveform generation, data collection and data analysis software are available upon request.